Dual interphase design stabilized Mg-metal batteries

Abstract

Rechargeable magnesium metal batteries (RMBs) promise high volumetric energy density and resource sustainability, yet interphase instability remains a central barrier to practical full cells. Here, we show that single-electrode interphase stabilization often does not translate into durable full-cell operation, as instability can still emerge at the counter electrode during cycling. We therefore propose an energy-level-guided electrolyte design using a dual-additive strategy that simultaneously programs the formation of both the anode solid-electrolyte interphase (SEI) and the cathode-electrolyte interphase (CEI). By aligning the electrolyte’s highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels with the cathode and anode potentials, the electrolyte undergoes spatially selective decomposition, enabling a continuous and uniform SEI/CEI pair. This programmed SEI/CEI pair expands the usable voltage window and supports deeper Mg2+ insertion/extraction, delivering 127.3 mAh g-1 (close to the theoretical capacity of Mo6S8, 128.8 mAh g-1) in Mg||Mo6S8 full cells, with cycling durability competitive with state-of-the-art RMB reports. These findings establish paired-interphase programming as a general design paradigm to break the capacity-lifetime trade-off in RMBs.